(A) Surface Treatment of Foils
Surface etching of aluminum and the formation of an oxide layer on the aluminum surface is known to prevent corrosion and increase the adhesion of additives, paints and colors onto the aluminium surface. Surface etching is commonly accomplished galvanostatically, whereby the surface of an aluminum foil/sheet is electrochemically modified by the combined use of a strong acid and a source of electricity. This method is also known as anodization.
Galvanostatic anodization is an energy intensive process. Moreover, in cases of processing thin aluminum foils, if the process is not controlled properly, the resultant anodized foil becomes brittle and crumbles. On the other hand, chemical etching of thin aluminum foils, under less controlled conditions damages the foil and creates holes within the foil material.
Etching of aluminum by wet treatment is conventionally used by aluminum finishers. Typical etching solutions comprise strong acids or an alkali metal hydroxide, usually sodium hydroxide, and a chelating agent.
(B) Production of Ultrafine Metal Oxide Nanofibres
Supported metal oxides are known to be used in several industrial, manufacturing commercial and environmental remediation processes. Transition metal oxides are useful in variety of applications such as catalytic synthesis of organic compounds and petroleum cracking. Catalytic performance in many of these processes is influenced by the catalytic surface area. Thus, nanometric sized catalytic particles is of significant commercial interest.
Using nanoparticles in form of a slurry requires a solid/liquid separation process to recycle the catalyst. The settling velocity of the nanoparticles is very slow, by virtue of higher surface area, and use of conventional gravity separators will result in long settling times which would likely result in uneconomical designs. Using a forced filtration process is possible, however energy is required for operation of a pumping system. Also, in most cases the presence of any remnant catalyst particle in the process stream is highly undesirable. Human exposure from handling the process stream during the slurry preparation process posses major occupational and safety problems.
Minimizing the limitations associated with using a slurry of catalyst particles has led to the development of immobilizing the catalyst particles onto a support medium. Chemical vapour deposition or coating a surface by dip coating with a slurry of nanoparticles and subsequently immobilizing the particles through thermal stabilization are the popular methods of producing a supported catalyst system. A major bottleneck of many catalyst supporting methods are related to the loss of surface area which is caused by the sintering or aggregation of the nano-catalyst onto the support surface during thermal treatment. Particle sintering results in the formation of large particles or a film/sheet on the support surface. This causes the catalytic surface area of the resultant supported catalyst system to be less than that of the discrete nanoparticles by a few orders of magnitude.
Electrospinning is a process of applying a high voltage to produce an interconnected membrane like web of small fibers with diameters in the nanometer range. This technique has been reported to be successfully utilized in the generation of thin fibers and the fabrication of large surface area membranes from a broad range of polymers, including engineering plastics, biopolymers, conducting polymers, block copolymers and polymer blends. The challenge in electrospinning processes is to control the process parameters to minimize the fiber diameter. Earlier studies have reported the formation of nanofibers with fiber diameters of the order of a few hundreds of nanometres. To date, however, there has been little success in forming ultrafine metal oxide nanofibres such as those having an average diameter of less than 100 microns.